Pivots: Weight on Sill and Nice Looking
Pivots have weight of the door on the sill. Nice looking wall mount pivots are available for the top of the door so it might seem that Pivots are always the way to go.

Drilling down into Curb:
However I am not crazy about drilling down into the curb if the curb is made out of wood.

Pivots Hold Less Weight
Hinges hang the weight of the door on the wall and yet some hinges such as the Vienna hold more weight than most pivots. Two Vienna's hold 36" door and 110 pounds. Two Horizon Pivots hold 32" Door and 100 pounds. Why is that? Pivots have all the weight of the door on one small point, the pivot pin.

Curb is Sloped
Also the curb is (supposed to be) sloped slightly. Pivots can handle the slope because the pivot pin doesn't spin so it can bend. But you can imagine the surfaces that actually hold the weight of the door cannot be very large. There is a small nylon washer between the base and the body and a spacer at the top of the pivot pin.

Pivots as Waterproof?
I believe they are. Vinyl and threshold can solve most any leakage problem whether you have pivots or hinges.

With Two hinges, the weight is distributed over a slightly larger area.
Should you use Pivots or Hinges?
My recommendation is to use the one that looks best to you while paying attention to the manufacturer's weight limits especially with Pivots.